use super::{RollingFileAppender, Rotation};
use e_utils::fs::FileShare;
use std::{io, path::Path};
use thiserror::Error;

/// A [builder] for configuring [`RollingFileAppender`]s.
///
/// [builder]: https://rust-unofficial.github.io/patterns/patterns/creational/builder.html
#[derive(Debug)]
pub struct Builder {
  pub(super) rotation: Rotation,
  pub(super) prefix: Option<String>,
  pub(super) suffix: Option<String>,
  pub(super) max_files: Option<usize>,
}

/// Errors returned by [`Builder::build`].
#[derive(Error, Debug)]
#[error("{context}: {source}")]
pub struct InitError {
  context: &'static str,
  #[source]
  source: io::Error,
}

impl InitError {
  pub(crate) fn ctx(context: &'static str) -> impl FnOnce(io::Error) -> Self {
    move |source| Self { context, source }
  }
}

impl Builder {
  /// Returns a new `Builder` for configuring a [`RollingFileAppender`], with
  /// the default parameters.
  ///
  /// # Default Values
  ///
  /// The default values for the builder are:
  ///
  /// | Parameter | Default Value | Notes |
  /// | :-------- | :------------ | :---- |
  /// | [`rotation`] | [`Rotation::NEVER`] | By default, log files will never be rotated. |
  /// | [`filename_prefix`] | `""` | By default, log file names will not have a prefix. |
  /// | [`filename_suffix`] | `""` | By default, log file names will not have a suffix. |
  /// | [`max_log_files`] | `None` | By default, there is no limit for maximum log file count. |
  ///
  /// [`rotation`]: Self::rotation
  /// [`filename_prefix`]: Self::filename_prefix
  /// [`filename_suffix`]: Self::filename_suffix
  /// [`max_log_files`]: Self::max_log_files
  #[must_use]
  pub const fn new() -> Self {
    Self {
      rotation: Rotation::NEVER,
      prefix: None,
      suffix: None,
      max_files: None,
    }
  }

  /// Sets the [rotation strategy] for log files.
  ///
  /// By default, this is [`Rotation::NEVER`].
  ///
  /// # Examples
  ///
  /// ```
  /// # fn docs() {
  /// use tracing_appender::rolling::{Rotation, RollingFileAppender};
  ///
  /// let appender = RollingFileAppender::builder()
  ///     .rotation(Rotation::HOURLY) // rotate log files once every hour
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  ///
  /// # drop(appender)
  /// # }
  /// ```
  ///
  /// [rotation strategy]: Rotation
  #[must_use]
  pub fn rotation(self, rotation: Rotation) -> Self {
    Self { rotation, ..self }
  }

  /// Sets the prefix for log filenames. The prefix is output before the
  /// timestamp in the file name, and if it is non-empty, it is followed by a
  /// dot (`.`).
  ///
  /// By default, log files do not have a prefix.
  ///
  /// # Examples
  ///
  /// Setting a prefix:
  ///
  /// ```
  /// use tracing_appender::rolling::RollingFileAppender;
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .filename_prefix("myapp.log") // log files will have names like "myapp.log.2019-01-01"
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender)
  /// # }
  /// ```
  ///
  /// No prefix:
  ///
  /// ```
  /// use tracing_appender::rolling::RollingFileAppender;
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .filename_prefix("") // log files will have names like "2019-01-01"
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender)
  /// # }
  /// ```
  ///
  /// [rotation strategy]: Rotation
  #[must_use]
  pub fn filename_prefix(self, prefix: impl Into<String>) -> Self {
    let prefix = prefix.into();
    // If the configured prefix is the empty string, then don't include a
    // separator character.
    let prefix = if prefix.is_empty() {
      None
    } else {
      Some(prefix)
    };
    Self { prefix, ..self }
  }

  /// Sets the suffix for log filenames. The suffix is output after the
  /// timestamp in the file name, and if it is non-empty, it is preceded by a
  /// dot (`.`).
  ///
  /// By default, log files do not have a suffix.
  ///
  /// # Examples
  ///
  /// Setting a suffix:
  ///
  /// ```
  /// use tracing_appender::rolling::RollingFileAppender;
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .filename_suffix("myapp.log") // log files will have names like "2019-01-01.myapp.log"
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender)
  /// # }
  /// ```
  ///
  /// No suffix:
  ///
  /// ```
  /// use tracing_appender::rolling::RollingFileAppender;
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .filename_suffix("") // log files will have names like "2019-01-01"
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender)
  /// # }
  /// ```
  ///
  /// [rotation strategy]: Rotation
  #[must_use]
  pub fn filename_suffix(self, suffix: impl Into<String>) -> Self {
    let suffix = suffix.into();
    // If the configured suffix is the empty string, then don't include a
    // separator character.
    let suffix = if suffix.is_empty() {
      None
    } else {
      Some(suffix)
    };
    Self { suffix, ..self }
  }

  /// Keeps the last `n` log files on disk.
  ///
  /// When a new log file is created, if there are `n` or more
  /// existing log files in the directory, the oldest will be deleted.
  /// If no value is supplied, the `RollingAppender` will not remove any files.
  ///
  /// Files are considered candidates for deletion based on the following
  /// criteria:
  ///
  /// * The file must not be a directory or symbolic link.
  /// * If the appender is configured with a [`filename_prefix`], the file
  ///   name must start with that prefix.
  /// * If the appender is configured with a [`filename_suffix`], the file
  ///   name must end with that suffix.
  /// * If the appender has neither a filename prefix nor a suffix, then the
  ///   file name must parse as a valid date based on the appender's date
  ///   format.
  ///
  /// Files matching these criteria may be deleted if the maximum number of
  /// log files in the directory has been reached.
  ///
  /// [`filename_prefix`]: Self::filename_prefix
  /// [`filename_suffix`]: Self::filename_suffix
  ///
  /// # Examples
  ///
  /// ```
  /// use tracing_appender::rolling::RollingFileAppender;
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .max_log_files(5) // only the most recent 5 log files will be kept
  ///     // ...
  ///     .build("/var/log")
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender)
  /// # }
  /// ```
  #[must_use]
  pub fn max_log_files(self, n: usize) -> Self {
    Self {
      max_files: Some(n),
      ..self
    }
  }

  /// Builds a new [`RollingFileAppender`] with the configured parameters,
  /// emitting log files to the provided directory.
  ///
  /// Unlike [`RollingFileAppender::new`], this returns a `Result` rather than
  /// panicking when the appender cannot be initialized.
  ///
  /// # Examples
  ///
  /// ```
  /// use tracing_appender::rolling::{Rotation, RollingFileAppender};
  ///
  /// # fn docs() {
  /// let appender = RollingFileAppender::builder()
  ///     .rotation(Rotation::DAILY) // rotate log files once per day
  ///     .filename_prefix("myapp.log") // log files will have names like "myapp.log.2019-01-01"
  ///     .build("/var/log/myapp") // write log files to the '/var/log/myapp' directory
  ///     .expect("failed to initialize rolling file appender");
  /// # drop(appender);
  /// # }
  /// ```
  ///
  /// This is equivalent to
  /// ```
  /// # fn docs() {
  /// let appender = tracing_appender::rolling::daily("myapp.log", "/var/log/myapp");
  /// # drop(appender);
  /// # }
  /// ```
  pub fn build(
    &self,
    directory: impl AsRef<Path>,
    share_type: FileShare,
  ) -> Result<RollingFileAppender, InitError> {
    RollingFileAppender::from_builder(self, directory, share_type)
  }
}

impl Default for Builder {
  fn default() -> Self {
    Self::new()
  }
}
